Burner and Method for Alternately Implementing Oxycombustion and Air Combustion

ABSTRACT

Fuel is combusted with an oxidizer and at least one mainly inert gas, where the mainly inert gas is injected in the form of a divergently swirled jet around the flame and a convergently swirled jet surrounding the divergently swirled jet.

The present invention relates to a burner and a combustion method whichcan make use alternately of a high-oxygen-content gas or of air asoxidizer.

With the increasingly stringent environmental restrictions, particularlyin terms of the production of CO₂ and NO_(x), the combustion of a fuelusing oxygen or a high-oxygen-content gas is becoming increasinglyattractive for the combustion of fossil fuels. However, the conventionalcombustion devices using air as oxidizer do not always have thegeometry, nor the requisite materials, for operating with oxygen or ahigh-oxygen-content gas. This is because the absence of the nitrogenballast in high-oxygen or all-oxygen combustion significantly modifiesthe heat transfer modes, the species concentrations, and the pressureconditions in the combustion chamber.

In order to operate with all-oxygen combustion in these installations,one proposed solution is to reinject flue gas produced by the saidcombustion or another combustion to partly make up for the absence ofnitrogen. This procedure serves to avoid a high production of NO_(x) dueboth to the absence of nitrogen, and also to a lower flame temperaturethan in all-oxygen combustion. However, the reinjected flue gas oftennullifies the benefits of oxycombustion, such as, in particular, thelower proportion of unburnts from heavy oil residues, or the decrease ofpart of the ash, these unburnts and this ash then causing complicationsin the downstream flue gas treatment method.

This flue gas injection can be made essentially in two ways. First, bymixing the said flue gas with oxygen before its introduction into theburner, so as to reconstitute an oxidizer comprising about 21 to 27%oxygen and the remainder essentially consisting of CO₂ instead ofnitrogen. One advantage that can be found for this solution in the caseof a conversion of an air boiler is the possibility of retaining the airburners with minor operating adjustments. On the contrary, the premixingof the flue gases with the oxygen before their introduction into theburner may give rise to safety problems. To avoid this problem, in asecond alternative, the flue gas can also be injected separately, eitherat a location of the combustion chamber, or through the burner. In thelatter case, the flue gas is injected at a velocity such as to lengthenthe flame, which may overheat the elements of the combustion chamber(opposite wall or tubes, in the case of a boiler). To avoid thisproblem, the flue gas injection velocities must be low, which has theeffect of increasing the size of the burner and of creating layoutproblems, whereas it is well known that the surface areas of thecombustion chamber must be maximized.

The preceding problems therefore imply the need to improve the methodsand the oxycombustion burners making use of flue gas recycling.

Furthermore, practice demonstrates the utility of being able to use thecombustion burners in flexible mode, that is, alternately inoxycombustion and in air combustion. In fact, owing to the restrictionsin oxygen availability and/or safety problems, it may be useful to beable to convert an oxycombustion into air combustion without replacingthe burner. Similarly, for certain types of combustion, it is preferableto start the combustion with air and then switch to oxycombustion forsafety reasons.

It is therefore the object of the present invention to propose a devicefor implementing an oxycombustion with flue gas recycle in a devicedesigned for an air combustion.

A further object of the present invention is to propose a combustiondevice for alternately implementing an oxycombustion with flue gasrecycle or an air combustion.

A further object of the present invention is to propose a combustiondevice for alternately implementing an oxycombustion with flue gasrecycle or an air combustion, the said combustions producing a flamehaving a controlled size.

For this purpose, the invention relates to a method of combustion of atleast one fuel using at least one oxidizer and at least one mainly inertgas, in which:

-   -   the fuel and the oxidizer are injected in such a way as to        create a flame,    -   the mainly inert gas is injected in the form of two jets, in        such a way that:        -   the first jet surrounds the flame created by the fuel and            the oxidizer and the said first jet has a divergent swirl            with regard to the said flame,        -   the second jet surrounds the first jet of mainly inert gas            and the said second jet has a convergent swirl with regard            to the flame created by the fuel and the oxidizer.

The invention further relates to a burner suitable for implementing thesaid method and comprising:

-   -   at least one means for injecting fuel and at least one means for        injecting oxidizer, the said means being placed with regard to        one another in such a way that the oxidizer and the fuel are        capable of producing a flame,    -   two means for injecting a mainly inert gas:        -   the first means for injecting the mainly inert gas being            suitable for injecting part of the mainly inert gas in the            form of a jet surrounding the flame produced by the oxidizer            and the first fuel, the said first means for injecting the            mainly inert gas comprising a means suitable for divergently            swirling the flow of mainly inert gas passing through it,        -   the second means for injecting the mainly inert gas being            suitable for injecting part of the mainly inert gas in the            form of a jet surrounding the jet of mainly inert gas            produced by the first means for injecting mainly inert gas,            and the said second means for injecting mainly inert gas            comprising a means suitable for convergently swirling the            flow of mainly inert gas passing through it.

Other features and advantages of the invention will appear from areading of the description that follows. Embodiments of the inventionare provided as non-limiting examples, illustrated by the FIG. 1 whichis a schematic view of a burner according to the invention.

The invention therefore relates to a method of combustion of at leastone fuel using at least one oxidizer and at least one mainly inert gas,in which:

-   -   the fuel and the oxidizer are injected in such a way as to        create a flame,    -   the mainly inert gas is injected in the form of two jets, in        such a way that:        -   the first jet surrounds the flame created by the fuel and            the oxidizer and the said first jet has a divergent swirl            with regard to the said flame,        -   the second jet surrounds the first jet of mainly inert gas            and the said second jet has a convergent swirl with regard            to the flame created by the fuel.

The method according to the invention implements the main combustion ofa fuel by an oxidizer. The fuel may be any liquid or gas type of fuel.If it is a gas, the fuel may be natural gas, mine gas, coke oven gas,blast furnace gas, refinery gas or syngas. If it is liquid, the fuel canbe selected from home-heating oil, heavy fuel oil, asphalt, refineryresidue, crude oil. The method may concern the combustion of a pluralityof fuel types, for example natural gas and liquid fuel oil. Thesevarious types of fuels are injected in such a way as to form a flamewith the oxidizer. The injections of the fuel or fuels and the oxidizercan be made in any manner known to a person skilled in the art in orderto produce a flame. According to the method of the invention, a mainlyinert gas is also injected. In the context of the present invention,“mainly inert gas” means a gas or a gas mixture of which the molarcomposition comprises at least 50% oxygen. In general, the mainly inertgas comprises at least one of the following compounds: CO₂, N₂, H₂O, Ar,preferably in a molar quantity of at least 50%. The type of mainly inertgas may be identical or different to that of the oxidizer according towhether the operating mode of the method is with air combustion or withoxycombustion. Regardless of the operating mode, the mainly inert gas isinjected in the form of two jets. The first jet surrounds the flamecreated by the fuel and the oxidizer, and the second jet surrounds thesaid first jet of mainly inert gas. In consequence, the second jet alsosurrounds the flame created by the fuel and the oxidizer, but is locatedat a greater distance from the flame than the second jet of mainly inertgas; in the application, mention is made of the first jet of mainlyinert gas as the inner peripheral jet, and mention is made of the secondjet of mainly inert gas as the outer peripheral jet. In the context ofthe present invention, “surround” means the fact that these jets ofmainly inert gas encircle the central flame of the fuel and theoxidizer. According to a preferred embodiment, the jets of mainly inertgas have the shape of rings centred on the flame of fuel and oxidizer.

According to the invention, the inner peripheral jet has a divergentswirl with regard to the flame of fuel and oxidizer. In the context ofthe present invention, swirl of a jet means a swirl movement of the jetabout itself. The inner peripheral jet is therefore a jet swirling aboutitself. Since the said jet surrounds the flame of fuel and oxidizer, thesaid inner peripheral jet is also swirling about the said flame.According to the invention, this swirl is divergent, that is, in theinner peripheral jet, the mainly inert gas moves away from the flame offuel and oxidizer as it is injected.

According to the invention, the outer peripheral jet has a convergentswirl with regard to the flame of fuel and oxidizer. Like the innerperipheral jet, the outer peripheral jet is also swirling about the saidflame. According to the invention, this swirl is convergent, that is, inthe outer peripheral jet, the mainly inert gas moves away from the flameof fuel and oxidizer as it is injected.

Whether for the inner peripheral jet or the outer peripheral jet, theswirl rate of each of these jets of mainly inert gas is advantageouslybetween 0.26 and 1.73. The swirl rate S is defined as follows: S=It/la,where It and la are respectively the tangential and axial pulses of thefluid swirled in a jet.

The method according to the invention serves to control the length ofthe flame by modifying the ratio of the flow rate of the peripheral jetto the flow rate of the inner jet.

The method according to the invention can be implemented both for anoxycombustion method and for an air combustion method. According to afirst embodiment of the method, it concerns an oxycombustion, whichmeans that one of the two oxidizers is an oxygen-containing gas. In thecontext of the present invention, oxygen-containing gas means a gashaving an oxygen concentration above 80%, preferably above 90%.According to this first embodiment, the oxidizer is an oxygen-containinggas and the mainly inert gas is composed of the flue gases from acombustion. The flue gases from a combustion generally comprise mainly,if not exclusively, CO₂. These gases may also comprise H₂O. Preferably,the mainly inert gas consists at least partly of the gases issuing fromthe combustion of the present method and which are recycled during thecombustion method. In this case, the flue gases are recycled outside thecombustion chamber in which the present method is implemented. They maybe treated before being recycled. In general, at least 4 Sm³ of fluegases are recycled during the method according to the invention.According to this first embodiment, it is preferable for the flow rateof mainly inert gas injected into the first jet of mainly inert gas toaccount for 50 to 97% of the total flow rate of mainly inert gasinjected. This distribution of the mainly inert gas between the innerand outer peripheral jets serves to avoid the rise of hot gases in thecombustion chamber. Furthermore, the gases issuing from a combustioninjected in the form of inner and outer peripheral jets do not disturbthe flame issuing from the combustion of the fuel and of theoxygen-containing gas, but create a corridor close to the nose of theburner which protects the walls of the combustion chamber fromexcessively intense radiation. Beyond the burner nose, the gases issuingfrom a combustion and injected in the form of inner and outer peripheraljets and the hot gases issuing from the actual combustion of the method,are mixed to form only one uniform mixture. According to a firstembodiment, gases issuing from a combustion may also be injected into atleast one point of the combustion chamber that is different from theinjection points of the inner and outer peripheral jets.

According to a second embodiment of the method, the method is an aircombustion method, which means that the two oxidizers are air (or noneof the oxidizers is an oxygen-containing gas). According to this secondembodiment, the oxidizer is air and the mainly inert gas is also air.Preferably, deoiled air is used, because this air flows in injectionmeans which may also serve for injecting an oxygen-containing gas inoxycombustion mode; the said injection means must therefore not comprisefatty matter in case of injection of oxygen-containing gas. Preferably,the flow rate of air injected as oxidizer accounts for 5 to 30% of thetotal flow rate of air injected into the method. It is also preferablefor the flow rate of air injected into the first jet of mainly inert gasto account for 4 to 25% of the total flow rate of air injected into themethod. Preferably, the total flow rate of air injected into the methodmay correspond to the quantity of air necessary for the combustion ofthe fuel. This distribution of the air flow rate in the inner and outerperipheral jets serves to make the air converge towards the fuel in sucha way as to connect the flame to the burner nose and to shorten it so asto prevent the overheating of the walls of the combustion chamber.

According to a third embodiment of the method, the oxidizer is anoxygen-containing gas and the mainly inert gas is air. This thirdembodiment is particularly used for the startup of the combustionmethod.

The invention also relates to a burner comprising:

-   -   at least one means for injecting fuel and at least one means for        injecting oxidizer, the said means being placed with regard to        one another in such a way that the oxidizer and the first fuel        are capable of producing a flame,    -   two means for injecting a mainly inert gas:        -   the first means for injecting the mainly inert gas being            suitable for injecting part of the mainly inert gas in the            form of a jet surrounding the flame produced by the oxidizer            and the fuel, the said first means for injecting the mainly            inert gas comprising a means suitable for divergently            swirling the flow of mainly inert gas passing through it,        -   the second means for injecting the mainly inert gas being            suitable for injecting part of the mainly inert gas in the            form of a jet surrounding the jet of mainly inert gas            produced by the first means for injecting mainly inert gas,            and the said second means for injecting mainly inert gas            comprising a means suitable for convergently swirling the            flow of mainly inert gas passing through it.

The burner according to the invention therefore comprises a firstcentral part comprising at least one means for injecting fuel and atleast one means for injecting oxidizer. These two injection means mustbe positioned with regard to one another in such a way that the oxidizerand fuel are capable of producing a flame when the burner operates. Thusthe means for injecting fuel and oxidizer may be coaxial tubes orseparate tubes. Any known technique for injecting fuel and oxidizer inorder to form a flame can be used.

The burner comprises a second peripheral part consisting of the twomeans for injecting mainly inert gas. The two parts of the burner may beadjacent, or separated by a partition. Preferably, the means suitablefor convergently swirling the flows of mainly inert gas passing throughthe first injection means or the second injection means causes the saidflows to swirl with a swirl rate of between 0.26 and 1.73. The saidmeans suitable for divergent or convergent swirling is generally adeflector.

According to a particular embodiment, the burner is such that:

-   -   the first means for injecting mainly inert gas comprises two        coaxial tubes centred around the means for injecting fuel and        the means for injecting oxidizer, the space between the two        tubes allowing the passage of part of the mainly inert gas and        comprising the means suitable for divergently swirling the flow        of mainly inert gas passing through it,    -   the second means for injecting mainly inert gas comprises two        coaxial tubes centred around the two coaxial tubes of the first        means for injecting mainly inert gas, the space between the two        tubes of the second means for injecting mainly inert gas        allowing the passage of part of the mainly inert gas and        comprising the means suitable for convergently swirling the flow        of mainly inert gas passing through it.

According to this particular embodiment, the burner may also comprisetwo means for injecting oxidizer, the said means being coaxial tubes,and the means for injecting fuel may be a metal ring drilled with atleast one ring of orifices, the said metal ring being coaxial with theoxidizer injection tubes and placed between the said tubes. The burneris then composed of four coaxial tubes and the metal ring drilled withorifices arranged in a ring, the said ring being placed between thesmallest tube and the tube having the immediately larger diameter.

According to the invention, the burner may comprise two distinct meansfor injecting fuel for the injection of two different fuels.

The invention also relates to a method for converting an air-fuel burnercomprising at least one means for injecting fuel and at least one meansfor injecting air, the said means being positioned with regard to oneanother in such a way that the air and the first fuel are capable ofproducing a flame, into an oxygen-fuel burner. The said conversionmethod consists in supplementing the said burner by two means forinjecting oxidizer:

-   -   the first means for injecting oxidizer being suitable for        injecting part of the oxidizer in the form of a jet surrounding        the air-fuel burner, and the said first means for injecting        oxidizer comprising a means suitable for divergently swirling        the flow of oxidizer passing through it,    -   the second means for injecting oxidizer being suitable for        injecting part of the mainly inert gas in the form of a jet        surrounding the air-fuel burner, and the said second means for        injecting oxidizer comprising a means suitable for convergently        swirling the flow of oxidizer passing through it.

It is thereby possible to convert an air-fuel burner into an oxygen-fuelburner for the combustion of the same fuel with an oxygen-containinggas. The conversion consists in adding to the air-fuel burner two meansfor injecting oxidizer. These injection means must be positioned in sucha way as to permit the injection of a first jet of oxidizer in a formsurrounding the air-fuel burner and the injection of a second jet ofoxidizer in a form surrounding the first jet of oxidizer and thereforethe air-fuel burner. Furthermore, these two injection means must beequipped with means for actuating them with a swirl movement: the jetclosest to the flame having a divergent swirl and the second aconvergent swirl.

The invention also relates to a method for converting a method of aircombustion of a fuel in which the fuel and the air are injected in sucha way as to create a flame, into an oxycombustion method, in which:

-   -   the air is replaced by an oxygen-containing gas, and    -   gases issuing from a combustion are injected in the form of two        jets, in such a way that:        -   the first jet surrounds the flame created by the fuel and            the oxygen-containing gas and the said first jet has a            divergent swirl with regard to the said flame,        -   the second jet surrounds the first gas jet issuing from a            combustion and the said second jet has a convergent swirl            with regard to the flame created by the fuel and the            oxygen-containing gas.

It is thereby possible to convert an air combustion method implementingan air/fuel combustion into an oxycombustion method implementing acombustion of the same fuel with an oxygen-containing gas. Theconversion consists in replacing the air by an oxygen-containing gas inthe initial method and in injecting the gases issuing from a combustionin addition to the said oxycombustion. The gases issuing from acombustion may be the gases issuing from the oxycombustion, which havebeen recycled, or may issue from another combustion. These gases issuingfrom a combustion must be introduced into the oxycombustion method inthe form of two jets both surrounding the flame created by the fuel andthe oxygen-containing gas, the second jet itself surrounding the firstjet. Furthermore, the first jet, which is the closest to the oxygen-fuelflame, must have a divergent swirl effect with regard to the flamecreated by the fuel and the oxygen-containing gas and the second jet,which is the closest to the oxygen-fuel flame, must have a convergentswirl effect with regard to the flame created by the fuel and theoxygen-containing gas.

FIG. 1 shows the end of a burner according to the invention. Itcomprises a first central part consisting of:

-   -   fuel injection means 1 which is a tube,    -   oxidizer injection means 2 which comprises two tubes 21 and 22:        one 21 is placed at the centre of the fuel injection tube 1 and        the other 22 around the same fuel injection tube 1.

The burner also comprises a second part which is a means for injectingmainly inert gas; it comprises three coaxial tubes 22, 31, 32 centred onthe first central part, the smallest tube corresponding to the tube 22for injecting fuel 1. The space between the largest tube 32 and theintermediate tube 31 comprises means 4 (fins) suitable for divergentlyswirling the flow of mainly inert gas passing through it. The spacebetween the intermediate tube 31 and the smallest tube 22 comprisesmeans 5 (fins) suitable for convergently swirling the flow of mainlyinert gas passing through it.

One advantage of the invention is that it serves to modify a burnernormally operating with air in such a way that it operates with anoxygen-containing gas and oxygen-containing flue gases. It suffices tosupplement the air burner corresponding to the first part of the burneraccording to the invention with the second part of the burner accordingto the invention suitable for injecting the recycled flue gases. Theoxygen-containing gas is then injected into the first part of the burnerand the flue gases are injected into the second part.

One advantage of the burner according to the invention is that it canoperate with air exclusively as oxidizer while preserving the flow offuel used for oxycombustion. This all-air operating necessity may berequired for continuing production in situations in which the oxygensupply to the burner is interrupted.

One advantage of the burner and of the combustion method according tothe invention is that they produce a flame having a controlled size,which is useful in confined vessels, such as boiler combustion chambersin which the direct contact of the excessively long flame with baresteel tubes is fatal. In this latter case, the geometry of the flameproduced by the burner according to the invention allows a uniformdistribution of the heat flux on all the inner surfaces of the boiler; aboiler equipped with this burner operating in oxycombustion canwithstand an energy density of up to 0.600 MW/m³ depending on theproportion of flue gas recycled.

A further advantage of the burner and of the combustion method accordingto the invention operating with an oxygen-containing gas is that theyproduce a flame having a high core temperature, whereby the unburnts aresignificantly decreased.

1-15. (canceled)
 16. A method of combustion of at least one fuel usingat least one oxidizer and at least one mainly inert gas, comprising thesteps of: injecting a fuel and an oxidizer to create a flame therefrom;injecting a mainly inert gas in two jets, wherein: the first jetsurrounds the flame created by the fuel and the oxidizer, the first jethas a divergent swirl with regard to the flame, the second jet surroundsthe first jet, and the second jet has a convergent swirl with regard tothe flame.
 17. The method of claim 16, wherein the oxidizer is anoxygen-containing gas and the mainly inert gas is comprised of gasesissuing from a combustion process.
 18. The method of claim 16, whereinthe oxidizer is an oxygen-containing gas and the mainly inert gas iscomprised of recycled gases from combustion of the oxidizer, fuel, andmainly inert gas.
 19. The method of claim 17, wherein a flow rate of thefirst jet accounts for 50 to 97% of a total flow rate of mainly inertgas injected.
 20. The method of claim 16, wherein the oxidizer is airand the mainly inert gas is air.
 21. The method of claim 20, wherein aflow rate of air injected as oxidizer accounts for 5 to 30% of a totalflow rate of air necessary for combustion of the fuel.
 22. The method ofclaim 20, wherein a flow rate of air injected into the first jetaccounts for 4 to 25% of a total flow rate of air necessary forcombustion of the fuel.
 23. The method of claim 16, wherein the oxidizeris an oxygen-containing gas and the mainly inert gas is air.
 24. Themethod of claim 16, wherein swirl rates of each of the jets is between0.26 and 1.73.
 25. The method of claim 16, wherein the jets arering-shaped.
 26. A burner comprising: at least one means for injectingfuel; at least one means for injecting oxidizer being placed with regardto said at least one means for injecting fuel such that the oxidizer andthe fuel are capable of producing a flame; and first and second meansfor injecting a mainly inert gas, wherein: said first means forinjecting the mainly inert gas is suitable for injecting part of themainly inert gas as a divergently swirled jet surrounding the flameproduced by the oxidizer and the fuel, said second means for injectingthe mainly inert gas is suitable for injecting part of the mainly inertgas in the form of a convergently swirled jet surrounding thedivergently swirled jet.
 27. The burner of claim 26, wherein: said firstand second means for injecting mainly inert gas comprise first, second,and third coaxial tubes centred around said means for injecting fuel andsaid means for injecting oxidizer; a space between said first and secondcoaxial tubes allowing passage of part of the mainly inert gas andcomprising a swirler suitable for divergently swirling a flow of mainlyinert gas passing therethough; and a space between said second and thirdcoaxial tubes allowing passage of part of the mainly inert gas andcomprising a swirler suitable for convergently swirling a flow of mainlyinert gas passing therethrough.
 28. The burner of claim 27, wherein:said at least one means for injecting oxidizer comprises said firstcoaxial tube surrounding, and coaxial with, an inner tube; said meansfor injecting fuel comprises a metal ring drilled with at least one ringof orifices; and said metal ring being coaxial with, and placed between,said first coaxial tube and said inner tube.
 29. A method for convertingan air-fuel burner into an oxygen-fuel burner, the air-fuel burnerhaving at least one means for injecting fuel and at least one means forinjecting air, the said means for injecting fuel and air beingpositioned with regard to one another such that the air and the fuel arecapable of producing a flame, said method comprising the steps of:providing the air-fuel burner; providing first and second means forinjecting mainly inert gas, said first means for injecting mainly inertgas being suitable for injecting a portion of mainly inert gas in theform of a jet surrounding the flame, said first means for injectingmainly inert gas comprising a swirler suitable for divergently swirlinga flow of mainly inert gas passing therethrough, said second means forinjecting mainly inert gas being suitable for injecting a portion of themainly inert gas in the form of a jet surrounding the flame, said secondmeans for injecting mainly inert gas comprising a swirler suitable forconvergently swirling the flow of mainly inert gas passing therethrough.30. A method for converting a method of air combustion of a fuel inwhich the fuel and the air are injected into a combustion space in sucha way as to create a flame, into an oxycombustion method, comprising thesteps of: replacing the air with an oxygen-containing gas; and injectinggases issuing from combustion into the combustion space in the form offirst and second jets, the first jet surrounding the flame created bythe fuel and the oxygen-containing gas and having divergent swirl withregard to the said flame, the second jet surrounding the first gas jet,the second jet having a convergent swirl with regard to the flamecreated by the fuel and the oxygen-containing gas.
 31. The method ofclaim 16, wherein the oxidizer is deoiled air and the mainly inert gasis air.
 32. A burner comprising: a first oxidizer injection tube; a fuelinjection device disposed coaxially around said first oxidizer injectiontube; a second oxidizer injection tube disposed coaxially around saidfirst oxidizer injection tube and said fuel injection device, saidburner capable of producing a flame through injection of oxidizerthrough said first oxidizer tube, injection of oxidizer through a spacebetween said fuel injection device and said second oxidizer injectiontube, and injection of fuel through said fuel injection device; a firstmainly inert gas injection tube disposed coaxially around said secondoxidizer injection tube, a first swirler being disposed in a spacebetween said second oxidizer injection tube and said first mainly inertgas injection tube, said first swirler being adapted to inject adivergently swirled jet of mainly inert gas therethrough that surroundsthe flame; and a second mainly inert gas injection tube disposedcoaxially around said first mainly inert gas injection tube, a secondswirler being disposed in a space between said first mainly inert gasinjection tube and said second mainly inert gas injection tube, saidsecond swirler being adapted to inject a convergently swirled jet ofmainly inert gas therethrough that surrounds the divergently swirledjet.
 33. The burner of claim 32, wherein said fuel injection devicecomprises a metal ring drilled with at least one ring of orifices.
 34. Amethod for converting an air-fuel burner into an oxygen-fuel burner, theair fuel-burner having a first oxidizer injection tube, a fuel injectiondevice disposed coaxially around the first oxidizer injection tube, anda second oxidizer injection tube disposed coaxially around the firstoxidizer injection tube and the fuel injection device, the burnercapable of producing a flame through injection of air through the firstoxidizer tube, injection of air through a space between the fuelinjection device and the second oxidizer injection tube, and injectionof fuel through the fuel injection device, said method comprising thestep of: providing first and second mainly inert gas injection devices,the first mainly inert gas injection device being suitable for injectinga first jet of mainly inert gas surrounding the flame, and the firstmainly inert gas injection device comprising a swirler suitable fordivergently swirling the flow of mainly inert gas passing therethrough,the second mainly inert gas injection device being suitable for a jet ofinjecting mainly inert gas surrounding the first jet, the second mainlyinert gas injection device comprising a swirler suitable forconvergently swirling the flow of mainly inert gas passing through it.35. A method of combustion, comprising the steps of: injecting anoxidizer and a fuel into a combustion space to create a flame; injectinga divergently swirled jet of mainly inert gas surrounding the flame; andinjecting a convergently swirled jet of mainly inerg gas surrounding thedivergently swirled jet.